In underwater breathing systems used by divers, the "push-pull" type breathing system supplies breathing gas from a remote source and returns exhaled gas to the source for CO.sub.2 removal and oxygen replenishment. This type of system increases diver's safety and productivity by eliminating the burden and possible danger inherent in closed circuit, back worn systems. The "push-pull" mode of operation allows the changing of CO.sub.2 absorbent canisters at the remote source of the gas, without interrupting the diver's work, in a single atmosphere control system that will suffice for several divers supplied from the same source.
For obvious safety reasons, such systems, as well as free-flow and demand systems, do require that backup units also be available in the event that there is interruption of the power and gas supply from the remote installation to the diver. In order to sustain the diver for at least a brief period of time in the event of a complete disruption of umbilical support, autonomous "bailout" systems are provided. Since such "bailout" systems must provide the necessary breathing gas for the diver independently of any connection to a remote location and remove carbon dioxide from the exhaled gas, these "bailout" systems typically include means for removing exhaled gas from the helmet, treating the exhaled gas to remove carbon dioxide and recirculating it to the helmet. In this system, as in all classic semi-closed mixed gas systems, oxygen is replentished by the controlled admission of gas mixtures.
A serious problem which however is encountered in autonomous "bailout" systems where there is a complete loss of umbilical power and heat, is the prevention of respiratory heat loss. Typically, bailout systems of the prior art have employed breathing bags with their inherent vulnerability to damage, flooding and heat loss, external hoses with inherent breathing resistance, heat loss and danger of entanglement, large, complex and heavy backpack equipment and externally mounted gas purification canisters which permit the heat generated by the lungs and the gas purification reaction to be dissipated without providing any warming of the inhaled gas.
It is accordingly an object of the present invention to provide a "bailout" system for use in underwater diving systems in the event of disruption of external support in which heat generated by the exothermic reaction occurring when carbon dioxide is absorbed from respiratory gas is used to warm the recirculated respiratory gas and surrounding environment inside the helmet, thereby preventing or at least minimizing respiratory heat loss.
Yet a further object of the present invention is to provide a "bailout" breathing system for underwater diving in which both heat and respiratory gas are preserved within the helmet.
Yet a further object of the present invention is to provide an emergency "bailout" system for underwater diving in which the gas recirculation system used including the means for purging carbon dioxide from exhaled gas is totally contained within the diving helmet thereby eliminating external tubes, canisters and other vulnerable encumbrances.